EN
ICCP system to vessel owners and operators is one of those workhorses you don't consider unless it stops working-which can be very costly, as it not only fails to combat the electrochemical corrosion of seawater on the hull, rudder and propeller but also accelerates it; resulting in additional maintenance costs for additional hull repairs during off-scheduled dry-docking periods and compromised structural integrity of ship components.
SME has been involved with troubleshooting, repairs and optimising ICCP systems on almost all major shipyards in China and abroad with more than 500 project installations and maintenance each year for the last 20 years. From our experiences we know the system’s performance does not fail due to single "catastrophic" reason but rather due to a combined degradation from the operational environment, component aging and various other factors. Below we look at the different elements of your ICCP system and highlight the most common causes for underperformance.
Anode condition and consumption
A key component of any ICCP system, the anodes, are designed to last many years unlike their sacrificial counterpart. However they are only functional as long as their mixed metal oxide(MMO) coating, which is on a titanium substrate, has not degraded or is depleted due to high output. Depletion causes increased resistance in the anode, uneven current distribution and eventually accelerated degradation in the anode's performance.
In our workshop at Nantong we often see anodes removed from ships after 5 to 7 years that have completely lost their coating in a localized section. This is frequently because an automatic control unit was over-driving intermittently; the system raises the voltage to compensate, overworking the remaining coating and consuming the remaining parts. A simple test of the anode potential, along with regular current output checks and anode mapping to detect any abnormal increase, can determine if your anode's coating is being degraded. Once every survey period should involve a thorough electrical impedance test not just a visual one.
Control unit sensitivity (including calibration and fouling)
The system works by monitoring the potential of your hull by using silver/silver-chloride reference electrodes. These half cells must provide a stable accurate measurement so the controller knows if it needs to increase or decrease DC output to keep the hull protected at the specified negative potential (-800 mV to -850 mV vs. Ag/AgCl). The main problem with reference electrodes is fouling; marine growth, slimes and calcification that insulate the sensing element and can slow response time; making voltage measurements inaccurate.
If a reference electrode is fouled it may measure a less negative voltage (e.g., -750mV) and so the ICCP will turn down, this can cause under-protection, accelerating corrosion on the hull. If a reference electrode is shorted electrically it could show as extremely negative (e.g., -1000mV) which can cause overprotection, the potential could damage the coating through hydrogen evolution and blistering. We have seen cases of both; the solution involves using reference electrodes with anti-fouling screens (either flush or guarded) and including reference electrode cleaning with your maintenance schedule. The reference electrode should also be validated using a portable calibrated half-cell on regular occasions and changed if the potential deviates more than 10 mV from your calibrated test half cell.
Control unit tuning and PID settings
Modern systems use controllers with a proportional-integral-derivative (PID) algorithm to maintain output. These controllers are not designed to be set and forget however; the condition of water will vary depending on the location-temperature, salinity, oxygen content, and speed of the ship will have a big impact on hull polarisation. If a controller is set for a ship in tropical waters and it travels to a brackish, colder, Baltic estuary the oscillation or delayed response will cause a problem.
We know from experience that it's more common to find that up to 30% of complaints concerning ICCP system performance are due to poorly tuned controllers. Indications of a problem are constant fluctuation between high/low current; high potential alarms and continuous running at max output. Fixing a controller often doesn't entail simply replacing it but means manually tuning it during a full voyage and logging on board so all conditions including ballast to load can be accounted for. Our technicians have data loggers specifically for tuning ICCP systems and can identify if adjustment to integral and derivative gains will correct the problem and return stable current output.
Hull coating condition
Many people overlook the link between hull coating and ICCP; an intact hull coating drastically reduces your current demand-by up to 60-70%. But once the anti-corrosive coating starts to delaminate or micro crack it creates a hull that has many 'hot spots' which then demand huge amounts of current from the anodes. This higher demand causes faster anode consumption and puts extra strain on the transformer/rectifier.
Moreover the anodes will not cover all the newly exposed steel evenly, meaning under-protection occurs in localized areas even though the overall system may appear to be functioning at normal output.
If you see a trend over successive dry-dockings showing an increasing current demand on your logs without the coating being updated, you will need an update of hull coating. It’s the most cost effective solution "performance upgrade" you can give an ICCP system.
Conclusion
Our 12-month warranty on each of our project services is not some marketing tactic but is based on the knowledge of our ability to properly diagnose the ICCP system. The entire system: anode, reference electrode, controller, coating and electrical conductivity of the hull are all interlinked; if one component is failing, it eventually leads to the degradation of the entire system. If you are already experiencing unexplained fluctuations—such as high/low potential alarms, increasing current demand, or coating damage—don't wait for your next scheduled maintenance.
The most common factors aren’t complex and in the event that your system’s performance is faltering, you need our team’s help to understand it fully. SME is able to achieve this at any location globally in any shipyard, for your ICCP requirements